Risk-assessment studies in rodents, felines and primates as to the potential for malignancy during a variety of normal physiology states are being done. The influence of pregnancy as well as other states of immunological suppression of this to viral induced malignancy, suggest response modification of the host during such normal physiological conditions. The expression of type C viral information by hormone and immunological fluctuations associated with reproductive processes justifies further studies to ascertain the risk of such a state to the laboratory worker.